This reverts commit dc427a47.

The change prevents migrating the entire range to VRAM because retry
fault restore_pages map the remaining system memory range to GPUs. It
will work correctly to submit together with partial mapping to GPU
patch later.
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>